To understand what each SMART attribute means check this Intel S.M.A.R.T Attributes. These attributes are specific to Intel SSDs, but nevertheless gives an idea, what kind of information SMART attributes convey. Some specific parameters may differ between different SSDs. Is LBA size one of them?, I don't know.

Especially, for Samsung 840 Pro (and may be even for other Samsung SSDs?) SMART Attribute Id 241 -- Total LBAs Written conveys this information. My guess for the LBA size is 512bytes, but I am not sure? Some experiments I ran by writing set amount of data to the SSD and measuring this attribute's value indicates it is 512bytes.

If the numbers are available via SMART, I find SMART a bit hit and miss, and it depends on the device. The other option on Linux is to monitor and record /proc/diskstats, though obviously that's reset on a reboot.
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mr.spuraticFeb 20 '13 at 17:40